What to build?

Everyone that has played minecraft has tried/wanted to build something they thought was awesome! So im wondering what you guys would build?

Me myself tryed to build a Star Destroyer xD Didnt workout well :S But I did make the washington monument!....Not much to brag about but myeh!

is there a pic of the monument ?

built a castle and at moment feels like excavating moria lol

Not that good at building yet, so I mostly build something that's grand, yet rather simple, sometimes imaginative like I made a grand stronghold for my house on one server, I even made an online server out of it really.

I like this, it's awesome.

Well I usually have big plans when making stuff, but is so time consuming i never get done.

I remmember i did make like a quite nice cave with running lava, smurf house, bathroom, treasure room, docks, farming a bigger doc and was impossible to break in unless you mined your way through so it was closed down with bistons and the like. This was all inside a giand mountain with tunel systems to the docks that also has smaller farms, to the living area, outposts to overwatch and to a large fielt that was closed in with large walls and lighted up where all pigs, hicken ad cows were breeded with iron golems to rid any ostile mobs besides creepers. Lots of torches!

Was a huge project as i planned from the start to build a large castle on the top of the mountain and expand the whole tunnel system. Unfortunatly the server file poofed. :<

As said I build in grand scale, yet very simple, I add detail work afterwards... My current great pride among structures would have to be on a different server of time where I've made a big and proper fortress with many small details, hidden rooms and the likes to it.